If your [Raspberry Pi](https://www.ampheo.com/c/raspberry-pi/raspberry-pi-boards) isn’t booting, follow this step-by-step guide to diagnose and fix the issue.

**1. Check Power Supply Issues**
**A. Verify the Power Source**
1. Use the official Raspberry Pi power supply (e.g., 5V/3A for [Pi 4](https://www.ampheo.com/search/Pi%204)/5).

2. Avoid USB ports from PCs or low-power chargers (may cause instability).

3. Check the LED indicators:

* Red LED (PWR): Should stay on. If blinking, power is unstable.
* Green LED (ACT): Should blink during boot. If off, SD card or OS issue.

**B. Test with a Different Cable & Adapter**
Some USB-C cables don’t deliver enough power (especially for Pi 4/5).

**2. Inspect the SD Card**
**A. Reflash the OS**
Corrupted OS? Reflash using:

* Raspberry Pi Imager (Download).
* Choose Raspberry Pi OS Lite (more stable for debugging).

**B. Try a Different SD Card**
* Faulty SD cards are a common boot failure cause.
* Use Class 10/UHS-I cards from reputable brands (SanDisk, Samsung).

C. Check SD Card Slot
Clean the contacts or try another card (some Pis are picky).

**3. Check HDMI & Display Issues**
**A. Test Another Monitor/Cable**
* Some monitors don’t support the Pi’s default resolution.
* Force HDMI detection (add to config.txt):

hdmi_force_hotplug=1  
hdmi_group=2  
hdmi_mode=82  # 1080p 60Hz  

**B. Boot in Headless Mode (No Display)**
Connect via SSH (enable it by placing an empty ssh file in the boot partition).

**4. Diagnose Hardware Problems**
**A. Look for Physical Damage**
Burnt components? Check for shorts, swollen capacitors, or overheating chips.

**B. Disconnect Peripherals**
Unplug USB devices, cameras, HATs—they may cause power issues.

**C. Check the Bootloader**
Pi 4/5: The bootloader may be corrupted.

Recovery steps:

1. Download the latest EEPROM firmware.
2. Flash it using another Pi or a PC with an SD card reader.

**5. Advanced Debugging**
**A. Check Boot Logs (Serial Console)**
* Connect a USB-to-TTL adapter (UART pins: TX, RX, GND).
* Use PuTTY (115200 baud) to see boot errors.

**B. Test with a Known-Good Pi**
Swap the SD card into a working Pi—if it boots, the original Pi is faulty.

**C. Power Supply Noise (Undervoltage)**
* Check for rainbow square (low voltage warning).
* Fix: Use a better PSU or powered USB hub.

**6. Common Fixes for Specific Scenarios**

**7. When to Give Up**
If none of the above works:

* Test with another Pi (if available).
* Contact Raspberry Pi support (if under warranty).
* Consider replacing if hardware is damaged.

**Final Tips**
✔ Always use a stable power supply.
✔ Backup your SD card (dd or [Raspberry Pi](https://www.ampheoelec.de/c/raspberry-pi/raspberry-pi-boards) Imager).
✔ Enable SSH for headless recovery.